Forces and springs:
Stretching and Bouncing
Supports National Curriculum, Key Stages 1 and 2 Unit 3E
Suitable for years 3, 4,5 and 6.
The time for whole session is about 45 minutes depending on the length of time spent on
examples.
Outline of content
Aims to
 establish what the children know through a fun demonstration
 explore elastic and inelastic properties of materials
 through class activities show that for elastic materials, the greater the force
applied the greater the extension
 also show: the thinner the elastic, the greater the stretch
 provide examples that will help to estimate the size of forces
 introduce springs and show they have elastic properties
 through examples show springs acting in compression as well as extension
 bring out that springs are useful- in particular they can save lives
Points to note:
Please read the notes about risks and agree the assessment with the teacher before
the session! (Link to risks at end of this file)
Particular care should to be taken when using springs and stretching elastic objects.
If stretched carelessly, elastic may break and flick back very painfully, but only the
eyes are at serious risk.
Cross References
- The slides in the PowerPoint presentation are referenced in the table.
- As the presentation may be running throughout the session some simple slides
provide a suitable background, alternatively switch to a black screen.
- Apparatus details are below the table and are linked to the relevant sections.
(link)
- Hints about risks are below the table (link here to list of hints)
Vocabulary: The presentation uses expressions included in the KS1&2 strategies
http://www.standards.dfes.gov.uk/schemes2/science/?view=get
Misconceptions – ie - Points that are often misunderstood
 Only ‘elastic’ is elastic.
 Plastic is a material rather than a property.
 Springs only work when stretched ie compression not understood.
Forces and Springs:
Stretching and Bouncing
1.
Activities
Discussion
Aims/facts
Show them the PEANUTS label
on the snake tin. Explain that you
have had a problem with the lid
and not been able to open it for a
while. Explain that one problem
with peanuts is that they get
worms in them. Then open the
tin, pointing it slightly forwards
so that the snake or worm springs
forwards.
(see apparatus list)
Ask the children what
has caused the worm to
spring out. They will
quickly explain that
there is a spring inside.
Continue the discussion
to find out what they
know. Show slide 2
which is animated.
Repeating the
demonstration often
helps. Include the
words pushes and pulls
in the discussion.
Discuss the changes in
length of the fashion
string
which
stays
stretched and the elastic
which springs back
when released. (See
safety notes.) Explain
that they show plastic
and elastic behaviour.
Show the animated
slides 3 and 4 to help
the discussion.
The elastic stretches to
many times its original
length. All the children
can feel that the force
on the elastic is
increasing as the length
increases.
Emphasise that the
children must carefully
pass the elastic back the
way it came. Discuss
the fact that the elastic
shrinks back to its
original length.
Establish what
the children know
about springs.
2.
Hand 2 lengths of ‘fashion string’
to each class group and ask each
group to pull one of the strings
and then compare it with the
unstretched one. Then hand out a
similar length of fishing pole
elastic and ask them to gently
stretch this.
(see apparatus list)
3.
Slide 5
Show a long length of fishing
pole elastic and pass the loop at
one end to the nearest child. Keep
hold of the loop at the other end.
Explain that they will have to be
very sensible and not let go of the
elastic. Also, they must not pull
very hard. Then ask the child
with the elastic to pass the end to
the next child whilst you keep
hold of the elastic. This should be
repeated so the elastic is threaded
round the class. Throughout the
game, keep hold of your loop and
before the tension becomes large
stop the game by releasing the
tension slowly.
(see apparatus list)
Plastic and elastic
materials
introduced.
The greater the
force the greater
the extension.
4.
5.
6.
7.
8.
9.
(see safety notes)
Show the class some
‘stretchimals’ or similar elastic
toys. Slide 6, 7
Hand two stretchimals with
different shapes to each group.
Ask them to stretch them by
slowly increasing the force
applied. Slide 8
(see apparatus list)
(see safety notes)
Explain that it is very useful to be
able to estimate the size of a
force. Slide 10 gives some useful
values that they can remember.
Slide 11
Ask the groups try to apply the
same pull to the two differently
shaped stretchimals. Show slide
12 and ask if the blue lizard will
be longer or shorter than the red
frog when the 10 newton force
pulls on it.
Slide 13, 14
Take the opportunity to re-cap.
Then use slide 14 to reinforce the
ideas.
Slide 15 – Springs
Explain that springs have elastic
properties.
Ask a volunteer to grip one end
of a ‘slinky’ spring firmly and
not to let go until you say.
Holding the other end of the
slinky, walk back across the front
of the class so that the ‘slinky’
stretches.
(see apparatus list)
Ask volunteers to stand in a line
and hold 4 or 5 similar springs.
Hang objects of different weights
on the springs. Compare the
amount the springs are stretched.
(see apparatus list)
10. Show a toy that has a spring in it
Discuss what they find
out. Take the
opportunity to discuss
their understanding of a
force.
Slide 9
Reinforce: the
greater the force
the greater the
extension.
This could be extended
if newtonmeters are
available to check
estimates.
Point out that the
‘greater the force, the
greater the increase in
length’ applies for all
the shapes. But the
thinner the toy the
longer the extension for
a particular size of
force.
Developing
estimating skills
Different
thicknesses
require different
forces to stretch
them by the same
amount.
Revision
Springs change length
when a force is applied
and return to their
original length when the
force is removed.
Larger forces cause
larger changes than
small forces.
Shaking the end of the
end of the spring so that
a transverse wave is
seen helps to get across
a message that ‘springs
can make things
happen’.
Use this as an
opportunity to estimate
the force on each
spring, e.g. an apple
will exert a force of
about 1 newton etc.
(This is an example of a
Springs have
elastic properties.
The larger the
force on the
spring the larger
the extension.
Springs can make
such as the woodpecker that
pecks as it slides down the rod.
Show the animated slide 16
(see apparatus list)
11. Ask for examples of where
springs are used.
Demonstrate examples of uses of
springs in toys, wind-up toys,
sports equipment e.g. a tennis
racquet etc and other items that
you have brought.
(see apparatus list)
(see safety notes)
12. Point out that some springs are
springy when they are squashed
rather than stretched.
( We say they are ‘compressed’.)
Show examples of objects that
use springs using slides 17 and
18 and hand round some
examples for groups to inspect.
(see safety notes)
Ask what happens to the shape of
a cushion or mattress as they sit
on a chair or get into bed.
13. Ask if they have been on a
bouncy castle and what would
happen if it was too hard or too
soft.
14. Show slide 19
15. Medical application: stents
Explain that springs save lives.
Show slide 20
Explain that stents are tiny
springs made of very special
metal that remembers its shape.
When a stent is squashed it later
springs back to its original shape.
16. Slide 21( animated so the steps
can be shown individually)
Explain that a special tube, called
a catheter, is threaded all the way
spring making a to-andfro movement possible.
It is called an
‘oscillation’.)
Use the discussion to
point out that there are
numerous examples and
many are hidden.
things happen.
Discuss examples.
Ask why the bed shown
in the cartoon (in slide
18) must be very hard.
They soon notice that
the mattress is
absolutely flat so the
weight of the character
is not enough to squash
the springs.
Some springs are
compressed when
forces are applied.
Unlike elastic
which only works
in extension.
Discuss examples of
springy surfaces that are
firm such as the surface
of a play area.
Discuss the examples.
Explain that some
people may have a
blockage which
prevents the blood
flowing round the heart.
A stent can be inserted
which keeps the artery
open so the blood can
flow.
Discuss the problems.
That the metal must not
corrode, that the spring
must be very, very
small.
During discussion
emphasise that this is
now a very common
procedure that makes
Some springs are
more firm than
others.
Springs are useful
Springs save lives
Physics (science)
saves lives.
through the arteries in the body
from the leg to the heart. The
catheter can be seen throughout
this process by special scans that
have been developed using
physics. When the catheter
reaches the correct position, a
tiny balloon pushes on the stent
so it opens the artery. The stent
then stays in place as the catheter
and balloon are withdrawn.
helps to reduce the
likelihood of heart
attacks.
Make the point that
many of the techniques
now used by the
medical profession have
been developed using
physics.
Slide 22
Safety Notes


Springs and elastic are unlikely to injure skin seriously: the odd nip can be
regarded as a learning experience. However, they may permanently damage
eyes. Eye protection should be worn whenever there is a chance that an elastic
cord or a spring may flick into the eye.
When demonstrating using the long length of fishing pole elastic, ensure that the
tension does not become large. If there is any misbehaviour avoid the exercise or
stop it immediately. Ensure that the tension is released gently.
Apparatus
1. Introduction
Jack-in-a-box type toy. E.g. a tin stating it contains peanuts but which has a
springy ‘worm’ in it. Available from on-line novelty suppliers or novelty shops.
2. Elastic and inelastic properties
 A pack of ‘fashion string’ as available from toy shops. (PVC ‘string’ used to
make plaited bracelets etc)
 Fishing pole elastic. Available from anglers’ suppliers. Lengths of ~10 metres
are sold for about £2. ( Buy 2 lengths and save one for use in activity 3.)
Cut the fashion string into lengths of about 30 cm so there are sufficient pieces for 2
pieces for each group.
Cut sufficient 30 cm lengths of fishing pole elastic so that there is one piece for each
group of 4 children.
3.
A long length of fishing pole elastic. Tie a loop at each end to serve as good
handles to hold the elastic firmly.
4.
Packs of stretchimals or similar latex toys available from on-line novelty
suppliers or novelty shops. Enough for two individual items of different shape
for each group of children.
8.
Slinky spring - available from school science labs or from on-line novelty
suppliers or novelty shops
9.


*
10, 11.
6 springs which stretch several centimetres when subjected to a 1 newton load.
(Any such available springs could be utilised. Alternatively, springs might be
borrowed from school science labs.)
Objects of various weights that can be suspended on the springs e.g. a lime, a
lemon, an orange and a grapefruit. These are familiar objects and their size is
closely linked with load on the springs.
Before the visit make string loops or other simple arrangements so that objects
can be suspended from the springs. If fruit is used, before the session, tie tapes
round the fruit so that it can be suspended from the springs.
Examples of familiar items with springs in them.
For example: toys including wind-up toys, sports equipment such as
tennis racquets, etc
Note: Examples of toys which have springs in them change rapidly. Look for examples
that are fun and novel!